1. Field of the Invention
The present invention relates to a push rod for operating valves in engines and more particularly to an oil-through type push rod for operating valves in internal combustion engines.
2. Prior Art
Conventionally, an oil-through type push rod has been manufactured by, for instance, an electrical resistance welding method. With this method, a metal end fitting(s) in which the end surfaces are formed into an arc-form of a concave or convex and an oil hole is formed is fastened to the circumferential edge of the opening at one or both ends of a steel pipe.
The conventional push rod of the oil-through type is, as described above, manufactured by welding metal end fitting(s) that has an oil hole(s) to a metal pipe. The most serious problem with such a push rod is that welding spatter that is inevitably generated during the welding is scattered and remains inside the pipe and that in view of the structure of the oil-through type push rod the spatter makes it difficult to clean the inner surface of the push rod.
The drawbacks of the push rods in which welding spatter remains inside thereof will be described below in detail. In other words, the drawbacks of an oil-through type push rod in which welding spatter remains inside the pipes and which is used in an engine assembly will be described below in terms of the manner of use:
1) First, when the engine is started, engine oil is supplied to the interior of the push rod via the oil hole formed in the end fitting, which is located in a position beneath the tappet.
2) The engine oil that is thus supplied passes through the interior of the pipe of the push rod and jets out of the oil hole of the upper end fitting, so that the oil lubricates the rocker arm and intake and exhaust valves that open the intake and exhaust passages, etc.
3) In this lubrication process, since the welding spatter is mixed with the engine oil, oil that contains such welding spatter is transmitted to the various sliding elements.
4) As a result, the welding spatter bites into the respective sliding surfaces of the rocker arm, intake and exhaust valves, etc., so that wear is accelerated, generating wear powder, etc. and shortening the useful life of the engine.
Accordingly, the present invention eliminates the above-described drawbacks with conventional oil-through type push rods.
It is an object of the present invention to provide an oil-through type push rod with a novel structure that prevents a welding spatter, that is generated and scattered during welding in cases where the oil-through type push rod is manufactured by welding a metal pipe and metal end fittings by, for instance, projection welding, from being left inside the pipe through which the engine oil passes.
The above object is accomplished by a unique structure for an oil-through type push rod which comprises a metal pipe and a metal end fitting that has an oil hole formed therein and is welded to the metal pipe, wherein the metal pipe is provided with a covering layer of a low-melting-point metal, and such a covering layer, which is for fixing a welding spatter generated during welding, is disposed on at least an inside wall surface of the metal pipe so as to be near an area where the metal end fitting is welded.
The above object is accomplished by another unique structure for an oil-through type push rod which comprises a metal pipe and a metal end fitting which has an oil hole formed therein and is welded to the metal pipe, wherein the metal pipe is provided with a covering layer of a low-melting-point metal, and such a covering layer, which is for fixing a welding spatter generated during welding, is disposed on at least an inside wall surface of the metal pipe so as to be near an area where the metal end fitting is welded; and the metal end fitting is provided with a covering layer of a low-melting-point metal, and such a covering layer, which is for fixing a welding spatter generated during welding, is disposed on at least an inside wall surface of the metal end fitting, the inside wall surface being an area where the metal end fitting is welded.